Vehicle manufacturers are increasingly replacing mechanical linkages in vehicles with sensors and electromechanical devices to reduce weight and cost. For example, sensors are replacing mechanical linkages to detect positions of user operated devices such as accelerator, clutch, and brake pedals. Signals are transmitted from the sensors to controllers and/or electromechanical devices in the vehicle. For example, a signal from an accelerator pedal may be transmitted to an actuator in the electronic throttle body to adjust the position of the throttle blade. Additionally, a throttle position sensor detects the position of the throttle blade and transmits a signal to an engine control module.
In cases where mechanical linkages are at least partially eliminated, multiple sensors are commonly used to perform redundant measurements and ensure system accuracy. For example, some manufacturers use analog position sensors that are based on a resistive ink or paste that is deposited on a non-conducting substrate. Other manufacturers use application specific integrated circuits (ASICs) in combination with sensors. The sensors typically include hall effect or inductively coupled sensors. The ASICs receive analog signals from the sensors and output pulse width modulated (PWM) or other types of signals.
Referring to FIG. 1, a vehicle control system 10 includes an accelerator pedal module 12, a control module 14, and an electronic throttle body (ETB) 16. The accelerator pedal module 12 includes first and second sensor modules 18 and 20, respectively, that communicate with the control module 14. The accelerator pedal module 12 also includes an accelerator pedal 22 that is in mechanical contact with the sensor modules 18 and 20. The sensor modules 18 and 20 are potentiometer-based sensors that include adjustable sensor resistances. During normal operations, a driver moves the accelerator pedal 22 between a minimum and a maximum position. For example, the accelerator pedal 22 may be in the minimum position when the driver does not make contact with the accelerator pedal 22. Accordingly, the accelerator pedal 22 may be in the maximum position when the driver presses down all the way on the accelerator pedal 22. As the accelerator pedal 22 moves between the minimum and maximum positions, mechanical contacts 24 between the accelerator pedal 22 and the sensor modules 18 and 20 adjust the values of the sensor resistances.
The sensor modules 18 and 20 generate respective position signals 26 and 28 based on the values of respective sensor resistances. The sensor modules 18 and 20 transmit the position signals 26 and 28 to the control module 14. The control module 14 determines first and second positions of the accelerator pedal 22 based on values of the position signals 26 and 28. The control module 14 may first convert values of the first and second position signals 26 and 28, respectively, into normalized position values representing a fraction of a range between minimum and maximum values of respective position signals 26 and 28. For example, the control module 14 may store values of the position signals 26 and 28 when the accelerator pedal 22 is set at predetermined positions during a calibration process.
Alternatively, the control module 14 may store minimum and maximum values of the position signals 26 and 28 that are learned during normal operations. This allows the control module 14 to determine the values of the position signals 26 and 28 by scaling between the preset values. Since the control module 14 determines multiple position values, the control module 14 may perform redundancy testing to verify the integrity of the sensor modules 18 and 20. The control module 14 adjusts a position of a throttle blade in the ETB 16 based on at least one of the value of the first position signal 26 and/or the value of the second position signal 28.
In the event of an electrical short-circuit between the first and second sensor modules 18 and 20, respectively, one or both of the values of the position signals 26 and 28 may become invalid, which adversely affects vehicle control. In one approach, the first sensor module 18 includes a short-circuit switch 30. When activated by the control module 14, the short-circuit switch 30 sets the value of the first position signal 26 to a predetermined value. For example, the value of the first position signal 26 may be set by shorting the sensor resistance of the first sensor module 18 to a reference or ground potential. While the short-circuit switch 30 is activated, the control module 14 compares the values of the first and second position signals 26 and 28, respectively. If the difference between the values of the position signals 26 and 28 is less than a predetermined value, it is likely that a short-circuit condition exists between the sensor modules 18 and 20 and the control module 14 may activate an alarm indicator.
The short-circuit switch 30 allows the control module 14 to periodically detect a short-circuit condition between the sensor modules 18 and 20. However, the accuracy of the values of the position signals 26 and 28 is compromised while the short-circuit switch 30 is activated. This interrupts other system diagnostics that utilize the values of the position signals 26 and 28 from the sensor modules 18 and 20. Additionally, the short-circuit switch 30 provides added cost and complexity to the sensor modules 18 and 20.